TC7116ACPL datasheet(9/14 Pages) TELCOM

9 / 14 page

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TELCOM SEMICONDUCTOR, INC.

negative supply for externally-generated segment drivers,

such as decimal points or any other presentation the user

may want to include on the LCD. (Figures 5 and 6 show

such an application.) No more than a 1 mA load should be

applied.

The second function is a "lamp test." When TEST is

pulled HIGH (to V+), all segments will be turned ON and

the display should read –1888. The TEST pin will sink

about 10 mA under these conditions.

DIGITAL SECTION

Figures 8 and 9 show the digital section for TC7116/

TC7116A and TC7117/TC7117A, respectively. For the

TC7116/TC7116A (Figure 8), an internal digital ground is

generated from a 6V zener diode and a large P-channel

source follower. This supply is made stiff to absorb the

relative large capacitive currents when the backplane (BP)

voltage is switched. The BP frequency is the clock fre-

quency

800. For 3 readings per second, this is a 60-Hz

square wave with a nominal amplitude of 5V. The seg-

ments are driven at the same frequency and amplitude,

and are in-phase with BP when OFF, but out-of-phase

when ON. In all cases, negligible DC voltage exists across

the segments.

Figure 9 is the digital section of the TC7117/TC7117A.

It is identical to the TC7116/TC7116A, except that the

regulated supply and BP drive have been eliminated, and

the segment drive is typically 8 mA. The 1000's output (pin

19) sinks current from two LED segments, and has a 16-mA

drive capability. The TC7117/TC7117A are designed to

drive common anode LED displays.

In both devices, the polarity indication is ON for analog

inputs. If V

–

IN and V

IN are reversed, this indication can be

reversed also, if desired.

Figure 8. TC7116/TC7116A Digital Section

TC7116

TC7116A

LCD PHASE DRIVER

THOUSANDS

HUNDREDS

TENS

UNITS

BACKPLANE

OSC

INTERNAL DIGITAL GROUND

–

TEST

6.2V

500

Ω

TO SWITCH DRIVERS

FROM COMPARATOR OUTPUT

CLOCK

VTH = 1V

7-SEGMENT

DECODE

7-SEGMENT

DECODE

7-SEGMENT

DECODE

200

TYPICAL SEGMENT OUTPUT

INTERNAL DIGITAL GROUND

SEGMENT

OUTPUT

0.5 mA

2 mA

LATCH

OSC3

OSC1

HLDR

70 k

Ω

LOGIC CONTROL

3-1/2 DIGIT ANALOG-TO-DIGITAL

CONVERTERS WITH HOLD

TC7116

TC7116A

TC7117

TC7117A

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